1. Field of the Invention
The present invention relates to a lighting device, a backlight unit, and a printed circuit board thereof, and more particularly, to a lighting device, a backlight unit, and a printed circuit board thereof including light emitting elements that can be driven in a sub-divided manner.
2. Discussion of the Related Art
Light emitting diodes (LEDs) are semiconductor light emitting devices that convert current to light so as to emit light. Since a red LED using GaAsP compound semiconductor was commercially available in 1962, it has been used together with a GaP:N-based green LED as a light source in electronic apparatuses for image display.
Further, the wavelength of light emitted from such an LED depends on the semiconductor material used to fabricate the LED, This is because the wavelength of the emitted light depends on the band gap of the semiconductor material representing an energy difference between valence-band electrons and conduction-band electrons.
In addition, a Gallium nitride (GaN) compound semiconductor is used in high-power electronic devices, because it exhibits a high thermal stability and a wide band gap of 0.8 to 6.2 eV. Further, it is possible to fabricate a semiconductor layer capable of emitting green, blue, or white light using GaN in combination with other elements, for example, indium (In), aluminum (Al), etc.
Further, it is possible to fabricate a semiconductor layer capable of emitting green, blue, or white light by combining GaN with other elements, for example, indium (In), aluminum (Al), etc.
Thus, it is possible to adjust the wavelength of light to be emitted by combining GaN with other appropriate elements. Accordingly, when GaN is used, it is possible to appropriately determine the materials of a desired LED in accordance with the characteristics of the apparatus to which the LED is applied. For example, it is possible to fabricate a blue LED useful for optical recording or a white LED to replace a glow lamp.
Because emission of white light is possible, the white light can be used for an illumination purpose. For example, white light can be used for a backlight unit of a liquid crystal display (LCD) device. Further, the LCD device, which is a light reception type flat display, has no ability to emit light by itself. Thus, the LCD device forms an image by using a backlight unit (BLU)
In more detail, a BLU includes a plurality of white LEDs arranged on a substrate such that light emitted from the white LEDs can be uniformly diffused. In more detail, FIG. 1 illustrates front circuit boards of a related art LED backlight unit. As shown in FIG. 1, six circuit boards 10 are mounted to a front surface of the backlight unit. Each circuit board 10 includes a plurality of mounts 11, to which LEDs are mounted, respectively, and connecting pads 12 arranged at one end of the circuit board 10, and electrically connected to the mounts 11.
In addition, shown in FIG. 1, the connectors 12 are arranged at opposite lateral ends of the backlight unit, namely, left and right ends of the backlight unit. Further, FIG. 2 illustrates the back surfaces of the circuit boards 10. As shown in FIG. 2, each circuit board 10 is connected to a drive board 30 via a connector 20 and connecting lines 21 under the condition in which the circuit board 10 is fixed to the backlight unit.
FIG. 3 illustrates a connected state of the connector 20. That is, FIG. 3 corresponds to a back surface of a portion “a” in FIG. 2. As shown in FIG. 3, each connector 20 includes a connector body 22, and first and second pins 23 and 24 provided at the connector body 22. The first pins 23 are connected to respective connecting lines, whereas the second pins 24 are connected to the connector 12 of the associated circuit board 10. Thus, the connector 20 connects the associated circuit board 10 to the drive board 30. Each first pin 23 is integral with an associated one of the second pins 24.
In addition, each connecting line 21 extends along the back surface of the associated circuit board 10, and is connected to the drive board 30. Because the circuit boards 10 are densely arranged, the connection of each connecting line to each connector 20 must be achieved only in a direction parallel to the plane of the associated circuit board 10, as shown in FIG. 3.
That is, in the related art backlight unit structure, the connectors 20 and connecting lines are arranged only at the left and right ends of the overall structure of the circuit boards 10, irrespective of the size of the backlight unit.
Therefore, the related art LED backlight unit cannot have a size freely variable in accordance with the size of the used LCD panel. Further, for a backlight unit having a small size, it is sufficient that the connectors are arranged only at one side of the backlight unit. However, for a backlight unit having a large size, there may be problems because the size of the circuit boards must be increased in proportion to the increased size of the backlight unit.
In addition, for an LED backlight unit, LEDs are mounted on circuit boards so that the circuit boards can be assembled to the backlight unit. Therefore, when each circuit board has an increased size, the number of LEDs mounted on the circuit board must be increased.
Meanwhile, the same type of LEDs have differences in terms of wavelength and brightness due to this characteristics. When such differences are increased, an increased color deviation occurs in the backlight unit. In addition for a large-size LED backlight unit using the above-mentioned related art circuit boards, the possibility that the color deviation occurs is increased, because an increased number of LEDs are used for one circuit board. As a result, the backlight unit with an increased size exhibits an increased defect rate.
In addition, for a large-size LED backlight unit using the above-mentioned circuit board, the possibility that the color deviation occurs is increased, because an increased number of LEDS are used for one circuit board. As a result, the backlight unit is manufactured with an increased defect rate.
Furthermore, the increased size of the circuit boards results in an increased size of equipment required for mounting LEDs and other elements on the circuit boards, where the equipment can be, for example, a surface mounting equipment such as a loader, a screen printer, a chip mounter, and a reflow device. Therefore, the cost of equipment is increased, especially because the prices of most surface mounting equipment are high.